Process of drawing formed structures of synthetic linear polyesters



June 12, 1951 A. PACE.,J'R 2,556,295

PROCESS OF DRAWING FORMED STRUCTURES OF.

' SYNTHETIC LINEAR POLYESTERS 2 Sheets-Sheet 1 Filed July 25, 1947 -TgDetermination for 0r stolline Polyjthylene T reph1halarte(?) 0. 6|

m E E= H 310 E 0.7l80 0.7IO0 o 40 8O I20 DEGREES CENTIGRADE F GINVENTOR.

v I ANDERSON PA GE, JR.

ATTORNEY.

Julie 12, 1951 A. PACE..JR PROCESS OF DRAWING FORMED STRUCTURES OFSYNTHETIC LINEAR POLYESTERS Filed July 23, 1947 2 Sheets-Sheet 2 PolyetDetermination for Amorphous 'aylene Teraphfrholofe SPECIFIC VOLUME ml/rn.

DEGREES CENTIGRADE FIG. 2

I I I1V1 ENToR. A NDERSON PA CE, JR.

ATTORNEY Patented June 12, 1951 2,556,295 PROCESS OF DRAWING FORMEDSTRUC- TURES F SYNTHETIC ESTERS LINEAR- POLY- Anderson Pace, Jr.,Buffalo, N. Y., assignor to E. I. du Pont de Nemours & Company,Wilmington, Del., a corporation of Delaware Application July 23, 1947,Serial No. 763,088

11 Claims.

This invention relates to the manufacture of shaped structures comprisedof linear superpolymers. More particularly it relates to a new andimproved method for drawing filaments, yarns, threads, ribbons, filmsand like shaped structures comprised of synthetic linear polyesters.

In the drawing of nylon yarn to enhance tenacity, i. e., tensilestrength, it is customary to draw in a single stage, and at an expedienttemperature, utilizing a draw pin to localize the drawing. Drawing ofnylon yarn in two stages has been suggested but since no advantage isrealized over a single-stage draw, and since there are obvious economicdraw-backs in-the operation of the two-stage draw the latter has neverbeen practiced commercially. The experience of the nylon art therefore,is that the drawing of yarn synthetic linear polymers is mostadvantageously accomplished in one stage. However, when the conventionalsingled raw procedure for nylon was used for drawing the newlydiscovered synthetic linear polyester yarns considerable difiiculty inobtaining uniform yarn properties and satisfactory operability wasencountered. Drawing at room temperature and somewhat above resulted inan unaccountable number of broken filaments and imperfectly stretchedyarn, while drawing at substantially elevated temperatures provederratic in the extreme in that the properties of the drawn yarn variedto a considerable degree, and results could not be duplicated from runto run.

This invention has as its principal objective therefore, the provisionof a satisfactory method for drawing filaments, yarn, thread, ribbon,film, and like shaped structures of synthetic linear polyester.

Another object is to provide a simple, economical method for uniformlystretching synthetic linear polyester shaped structures to achievemaximum tensile strength without sacrifice in quality.

Another object is to produce stretched filaments, yarn, thread, ribbonand film of synthetic linear polyester which structures arecharacterized by uniform optimum physical properties including hightenacity.

A further object is to draw filaments and yarns of synthetic linearpolyesters so as to achieve maximum tenacity and improved physical andchemical properties with a high degree of uniformity.

,A still further object is to produce filaments and yarns of syntheticlinear polyesters having enhanced tenacities, improved transverseproperties, improved resistance to acids and alkalis, im-

Briefly stated the present invention comprises first drawing a formedyarn of synthetic linear polyester at a temperature between the secondorder transition temperature (represented herein by the symbol T3) andthe apparent minimum crystallization temperature (represented herein bythe symbol T1) and thereafter further drawing the yarn at a temperatureabove, and preferably at least 50 C. above, the apparent minimumcrystalization temperature (T1) to give a yarn of maximum tenacity. Ifdesired, the drawing operation may be followed by a hot relaxing step tosecure an increased elongation in the finished yarn.

In the annexed drawings Figs. 1 and 2 are graphical illustrations ofrepresentative determinations of the value of the second ordertransition temperature (Tg) for a representative synthetic linearpolyester, viz., polyethylene terephthalate.

To facilitate an understanding of the invention reference should be hadto the following definitions and explanations of terms, it beingunderstood that these terms whenever employed in the followingdescription and claims are to be construed in accordance with suchdefinitions and explanations.

By the expression synthetic linear poly-.-

ester(s) is meant a linear polyester having an intrinsic viscosity of atleast 0.3, a low degree of solubility in organic solvents and having thefurther characteristic property when formed into filaments of-beingcapable of being cold-drawn to the extent of at least two times theoriginal filament length to form useful textile fibersof strength andpliability.

critical great I 3 The expression intrinsic viscosity, denoted by thesymbol no, is used herein as a measure of the degree of polymerizationof the polyester and may be defined as:

limit 6+ as O approaches zero wherein m is the viscosity of a dilutephenoltetrachloroethane (60:40) solution of the poly-- is theconcentration in grams of the-polyester per 100 cc. of solution.

The expression second order transition temperature, (Tg), is defined as-the temperature atwhich a discontinuity occurs in the-curve of a firstderivative thermodynamic -quan'tity:withtemperature. It is correlatedwith yield temperature and polymer fluidity and can be ob-- served froma plot of density, specific volume, specific heat, sonic modulus orindex of refraction against temperature.

For the purpose of this invention, a satisfactory method for measuringthe second order transition temperature is as follows:

A plug of the polymer to be tested is formed. The plug should preferablybe formed from the melt and rapidly cooled so that it is obtained in theamorphous form. It is then weighed in air and fitted for hanging from abalance. The plug is so suspended from the balance that it hangscentrally in a bath of silicone oil and l below the surface. Thetemperature of the bath is thermostatically controlled. A silicone oilis especially desirable because of the excellent stability and lowprobability of attack on polymer specimens. A thermometer calibrated in0.l C. is placed in the bath with the polymer plug to measurethetemperature. The bath is held at a given temperature until thepolymer plug in the silicone oil has reached a constant weight. The plugnormally reaches the value within 15 minutes. After the balancereading-is made, the temperature is raised 10 C. and the processrepeated. Usually a temperature range of approximately 0-160 0. givesenough points to allow calculation of Tg. This-range is obviouslydetermined by polymer type.

From-the weight of the polymer plug in air and in silicone oil, it ispossible 'tocalculate density and specific volume at a given-temperature. Corrections are made for the buoyant efiect of air on the polymerplug. The equation used in calculation is:

where Vp=specific volume of polymer, p=density of polymer ps=densityof'silicone oil, Wv=weight of polymer in vacuo, Ws=weight of polymer insilicone oil.

The portions of the curveof specific volume vs. temperature above andbelow Tg are linear as shown in Figs. 1 and 2. The coefiic'ient's ofexpansion are calculated from the slopes of the curve.

tensions of the twolinear portio'nsof the curve intersect. Figures 1 and2 show graphically how Tg for a representative polyester is determined.Figure 1 refers to crystalline polyethylene terephthalate while Figure 2refers to the amorphous form of the same polymer.

For an accurate determination of operating draw temperatures, it ispreferred to measure Tg for amorphous polymer since polyesters, asspunor cast, are quenched so rapidly that little or no crystallization takesplace. Since Tg increases as the degree of crystallization of thepolymer increases, the true draw temperature range of as-spun yarn orfilm is better delineated if the determination is run using amorphouspolymer. Of course if a crystalline or partially crystalline polyesteris normally obtained in the-as-spun state a Tg determination should berun, using as-spun polymer. This will give a more accurate lower limitfor the actual primary draw temperature.

The expression apparent minimum crystal lization temperature, (Ti), isdefined as the lowest temperature at which a marked rate of densitychange, which is known to occur simultaneously with crystallization,takes place within six hours. apparent minimum crystallizationtemperature a sample of polyester maintained constant at saidtemperature below T1 will not vary substan tially in density over a longperiod e. g., six hours.

However, as soon as the polyester is subjected to the temperature T1there occurs a rapid changev in density. Acutally the rate changes quiteabruptly from no change in six hours to a change within minutes for onlya few degrees temperature difference. The value of T1 is convenientlyassigned from density determinations done in airor silicone oil and isbased on crystallization by heat only.

Since a change in density accompanies the mechanism of crystallization,it is only necessary to determine the temperature at which a significantchange in density occurs. Thus, the temperature at which the density ofthe polymeric material starts to rapidly increase may be takenas theapparent minimum crystallization temperature. A suitable apparatus withwhich to measure the density of polymeric materials is that of a densitygradient tube. Briefly, one

embodiment-may consist of a long tube filledwith' partially mixed carbontetrachloride and toluene, so that a density gradient of 0.86-1.59grams: per

milliliter is maintained-from top to bottom of the tube. After propercalibration of density vs. position, the tube can be used to measuredensities of polymeric materials by determining the position ofsmallsamp'les in the tube. The method is especially applicable to heavydenier monofils, since with multi-filament yarns, there'is always thepossibility of small bubbles of air-being entrapped, which will tend togive inaccurate density readings.

To measure T1 several small pieces of monofil- (appro'xim'ately 10grams) of the amorphous synping a piece of the 'monofil into the densitygradient tube andallowing it to reach an equilibrium height.- Thisoccurs-within about 15 min.

For every temperature below the utes and does not allow enough time forswelling by the 0014- toluene mixture. At various time intervals up to 6hours, density measurements are made and the density is plotted againsttime to show the rate of crystallization. Below the apparent minimumcrystallization temperature, this graph will normally show a straightline with no apparent increase in density of the polymeric material overthis period of time. Simultaneously, other samples may be run atincreasing temperatures say in steps of 2, 5, or .The plot of densityvs. time, will in nearly all cases, be substantially a straight lineuntil the apparent minim-um crystallization temperature is exceeded, atwhich time the density will increase over a period of time until amaximum order of crystallinity is reached and the curve will againflatten out. This procedure will give a temperature range as anapproximation of T1. Further density determinations are carried. out inthe vicinity of this approximate temperature using smaller temperatureincrements of the order of 0.5-l.0 to determine accurately the apparentminimum crystallization temperature. Depending upon the accuracy of theapparatus used and the care with which the procedure is followed, T1 isordinarily reliable to within 1 or 2.

The type of synthetic linear polyester hereinabove defined whichresponds to treatment in accordance with the principles of thisinvention may be formed by any of the general processes described inUnited States Patent Nos. 2,071,250 and 2,071,251 (Carothers), e. g., bythe action of dihydric alcohol, such as glycol, on a suitable bibasicacid, such as terephthalic acid, or dibasic acid derivative such asdimethyl terephthalate. As specific examples of synthetic linearpolyesters contemplated for purposes of this invention. there may bementioned high molecular weight linear polymers of ethyleneterephthalate, of trimethylene terephthalate, of tetramethyleneterephathalate, of hexamethylene terephthalate, etc.; the linearpolymers of polymethylene diphenoxy-n-alkane-4 :4 -dicarboxylatesdisclosed in Dickson application Serial No. 638,485, filed December 29,1945, now U. S. No. 2,465,150; the

in Cook,

I-Iuggill, and Lowe application Serial No. 708,440,

filed November 7, 1946, now abandoned; the linear polyesters derivedfrom p-(hydroxymethyl) -benzoic acid and similar hydroxy carboxylicacids disclosed in Cook, Dickson, Lowe, and Whinfield application SerialNo. 711,470, filed November 21, 1946, now U. S. Patent No. 2,471,023,and the linear polyesters polymethylene-diphenylthioether 4:4dicarboxylates and the like disclosed in Lowe application Serial No.708,442, filed November 7, 1946, now abandoned. A preferred polyester,particularly suited to yarn manufacture, is polyethylene terephthalateand the invention will be further described with specific reference tosaid polyester. It is to be understood however, that my inventioncontemplates the two-stage drawing in like fashion of any member of theclass of synthetic ,esters previously defined.

linear poly- Fiber-forming synthetic linear polyesters should possess anintrinsic viscosity of at least 0.3 and preferably should have anintrinsic viscosity of from 0.3 to 1.5. Polymers having an intrinsicviscosity less than 0.3 do not form commercially-acceptable fibers. Boththe transition temperatures and the degradation temperatures are too lowto be useful. The intrinsic viscosity of the polyester is one of themain determining factors with regard to Tg and T1. Generally, as theintrinsic viscosity increases Tg increases until a maximum value isreached. Any increase in the intrinsic viscosity above a certain valuewill not appreciably increase Tg. The following table shows the relationof Tg to intrinsic viscosity for a representative crystalline polyester,i. e. polyethylene terephthalate:

Table I 51. 0 0. 24 57. 0 0. 2s 70. 5 0. 4o 81. 0 o. 51 80.0 0. 61 so. 0o. 81. o o. 76

Synthetic linear polyesters in the amorphous form exhibit a similarchange of Tg with respect to increasing intrinsic viscosity. It isimportant to remember, however, that for a given intrinsic viscosity, Tgfor, an amorphous polyester is not the same as Tg of a crystalline one.Actually, Tg increases as the crystalline-amorphous ratio increases. Forexample, polyethylene terephthalate with an intrinsic viscosity in thevicinity of 0.70 has a Tg in the amorphous state of 67 C. while the samepolymer exhibits a Tg of 80 C when crystalline.

It is generally true that when a synthetic linear polyester is spun orcast and rapidly quenched from the molten state that the formedstructure is almost totally amorphous. Quite conceivably a spun or caststructure could be cooled slowly and would, therefore, be in thetemperature range inducing crystallization (above T1) for a considerablelength of time. Therefore, in such a case the polymer would bepredominantly crystalline and exhibit a Tg considerably higher than thatof the amorphous form.

This latter possibility, however, will not generally be met incommercial operations since the as-spun yarn is cooled so quickly thatit has little or no chance to crystallize. In any event it is notdesirable to start with a partially crystalline yarn or film since it isdifficult to secure the alignment desired in orientation when the freemovement of the molecules in the polymeric structure is restricted bycrystal formation. However, even if the as-spun yarn is partiallycrystalline it can be drawn by this two-stage process by paying strictattention to its Tg criterion.

Continuous filaments and yarns of the highly polymeric linear esters ofthis invention are best prepared by melt spinning the polyesters, e. g.melting chips'of synthetic linear polyesters on a heated grid, passingthe melt through a filter bed made up of a number of small particles,such as sand, forcing it through a spinneret and cooling the filamentsso formed. When melt spinning these polymeric esters, it is necessaryfor the esters to be substantially water free if hydrolysis of thepolyesters during thisprocess is to be avoided. Filamentsmay alsobeformed from solutions of these polymeric esters using any of thesolution spinning processes known.

in the art; suitable solventsfor these: polymeric esters are cresol,nitrobenzone andchlorinated compounds, such as tetrachloroethane, etc;

Films of these synthetic linear polyesters are best prepared byextrusion of the molten polymer through a suitable shaped orifice andthen quenching the molten material. Inthis'process the film may bequenched on extrusion by jets of cold inert gas, e. g. air, immersion ina liquid, e. g. water or by contact with one or more metal surfaces,which surfaces. may themselves be cooled by jets of gas or immersioninliquidsu The filmmay. also be extruded, if desired,'as a largediameter tube having thin. walls, which tube may be flattened and oncutting provide one or more films. In the latter method of working, thecooling is carried out very satisfactorily by jets of inert gas. It ispreferred that these films are stretched after extrusion while they arebeing quenched, in order that unduly, narrow orifices are not requiredfor the extrusion of thin films. Films may also be prepared fromsolution of the polymeric esters by evaporating the solvents from thinlayers of solution at temperatures below the boiling point of the.solvent. Solvents for the solution spinning process described hereinbefore may be used.

As stated previously the synthetic linear polyester structure is given afirst or primary draw while the structure is at a temperature between Tgand Ti, and preferably in the vicinity of Tg. Maximum orientation shouldbe obtained by the primary draw. The final, or secondary draw is givenwhile the polymer structure is at a temperature above Tl. For the sakeof efiiciency and to secure maximum crystallinity with contact timescommensurate with present day high speed drawing operations e. g., m ofa second or less for yarn, it is necessary to raise the temperature ofthe polymer structure to a value at least 50 higher than its apparentminimum crystallization temperature for the secondary draw. If maximumcrystallinity is not desired the secondary draw may be imposed at lowertemperatures above the apparent minimum crystallization temperature.

It is preferable, but not essential, to secure. maximum orientation ofamorphous yarn in the vicinity of the primary draw temperature ifoptimum yarn properties are desired. The higher the degree oforientation in the yarn, the higher the crystallization temperaturewhich can be used to secure a high degree of crystallinity at economicalspeeds of operation. Conceivably, of course, a non-oriented amorphousyarn may be heated to a point where crystallization. takes place withoutseriously degrading the yarn, e. g. in the vicinity of 108 C. a fairlyhigh degree of crystallinity may be achieved by this process but theyarn tenacity and elongation will generally not be in a range useful fortextile purposes eX- cept, perhaps, for very special applications.

The drawing of synthetic linear polyester yarns is preferably done sothat the combination of initial and final draw ratios, depending uponthe individual polymer, imposes a stretch of from 310 and more times theoriginal length of the yarn and preferably from 5-8 times-the originallength of the yarn. As mentioned previously,

the drawing is preferably accomplished so that total orientation of theamorphous structure is achieved during the primary draw followed bycomplete or nearly complete crystallization during .the. secondary draw:

cosityin: thevicinityofOfi, thisv can be accoma.

plishedby-adraw ratio of about-4:1 at the pri.-..v mary draw:temperature, .as. hereinbefore defined,;

followed-bye 1.5:]. drawratio at a temperature in excess-.of 50 aboveTi.

maybeused to increase the tenacity of the yarn. The preferred ratioswill be dependent to a large; extent onthe ultimate use of the yarns soprocessedz;v By hot relaxingtheyarn various amounts.

aftendrawing, physical properties, such as tenace.

ity, elongation, and work recovery, maybe fur.-

thenchanged through wide limits.

The drawing tension for the primary draw may; Thelsecondary draw,although carried out at. a higher. temperature; requires. more force:and.-.is.in.the range of 0.1 g./denier. to. the breaking tensions be inthe range of 0.05-1.5 g./denier.

The exact tension .to be used depends on the amount of draw beingaccomplished in each;

stage.

The drawing of synthetic linear. polyester yarns; may be carried: out bythe use of hot rolls, heated; These. various:

draw pins, or heated.v chambers. methods are well-known and only needthe coordinating of details by one skilled in the artto worksuccessfully. The yarn may be packaged,

between the primary. and secondary draw or pref-.-

erably it may be run in a continuous, manner,

from the primary draw to the secondary. It may: alsobe. desired to hotrelax the yarn 0011-,

tinuously after the secondary drawand in this.

manner. a completelycontinuous process may be obtained.

A convenient method for the orientation of. film is by the extrusion.ofa large diameter tube of synthetic linear polyester from a disk which.

od is to. extrude the film from a slot orifice:

Then'the film is drawn longitudinally by means of a pinch'roll systemand at the same time is drawn; laterally by means of clamps which arefastened at both edges of the film and move apartas the film is drawnlongitudinally by the action of the pinch roll. This film, during thetwo-dimensional drawing, may be heated by pass.- ing over heated rollsduring drawing or by means of hot, inert gases or liquids or byinduction.

heating. While it is preferred that. two-dimensional orientation of thefilms of this invention takes place in two directions at once, this isnot essential. A film may be drawn, for example, between two sets ofrolls, first in one direction and then in another.

This invention is further illustrated by the fol-. lowing exampleswherein are set forth preferred modes for practicing the principles ofthe invene tion and the many advantages derived therefrom.

EXAMPLE I Polyethylene terephthalate yarn is passed through suitableguides to a heated roll (79 C. to C'.) which has a peripheral speed of60 feet per minute and several wraps are made about it to preventslippage. The yarn then passes to a :second cold roll (35 C. to 50 C.)

which acts as the initial drawroll. The second In. the caseofipolw;ethylene. terephthalate. having, .an intrinsic.-

Of course, it will be. realizedthat other-combinations. of draw ratios.

9 roll has a surface speed of 4.4 to 6.2 times that of the first rolldepending on the initial draw ratio desired as shown in the table below.Several wraps are made around the second roll to prevent slippage andthe yarn passes over a hot curved plate (160 C. to' 180 C'.) to a thirdroll which acts as the secondary draw roll. The third roll is cold andhas a peripheral speed of 1.36 times that of the second roll. Severalwraps are made around the third roll and the yarn then passes around acork faced driven roll to prevent slippage and the yarn is then taken upon a down-twister. In the following table various Another type ofdouble-drawing apparatus that may be used to obtain the improvement ofthe process of this invention demonstrated by the following examples: I

A 1200 denier, 70 filament polyethylene terephthalate yarn (T =80 C.;Ti=99 0.) prepared from polymer having an intrinsic viscosity of 0.61 ispassed over a snubber feed roll to a hot pin (100 C.) --Two wraps'aremade about this pin and then "the yarn passes immediately over a 3 hotplate (180 C.) and then t the draw roll which has a peripheral speed(corresponding to the desired draw ratio) faster than the feed roll.Three .or more wraps are made about the draw roll to prevent slippageand then the yarnpasses to an appropriate yarn takeup device. The tablebelow shows the exact conditions at each step in the process for thisapparatus as well asi'the'icomparative properties:

' Copolymers of polyesters also may be spun into fibers, yarns, etc. andthese structures may also be double-drawn under the conditions outlinedherein to give improved structures. For example, a mixed polyesterprepared by reacting terephthalic acid, ethylene glycol and diethyleneglycol *under polymerizing conditions may be spun using conventionalmelt-spinning techniques to give a drawable yarn. The following tableshows the improved properties obtained by double-drawing a yarn preparedfrom a representative copolymer of terephthalic acid, as compared tosingle-stage drawing of the same copolymer.

Table II [Control] Yam 1 2 1 3 4 Intrinsic Viscosity (no) 1st Stage Drawand Temp 0 0.6 0. 7

1st Stage Draw and Temp 6 0 1 (85) 5. 44: (85) 4. :1 (85) 4. 85:1 (85)2nd Stage Draw and Temp 1.36:1 (180) 1. 36:1 (180) 1. 36:1 (130).

Total Draw 6. 0:1 7.421 6.021 6.6:1 -Relaxation (75) Temp. (C.)

Dty Tenacity (g. p. d.) 6.8 8.1 8. 1 8- 7 "Dry Elongation, Per Cent 9.38.2 8.2 y 7.8

; From the above examples, it is obvious that Table IV thedouble-drawing process results in improved yarn. While the increase intenacity is important, Yamm 1 2' the improved operability, whichaccompanies this I process, is also very desirable. This is rather 40gem Temp. at pin draw point o. 9 so raw ratio at pin 5.6 6. 2:surprising s nce the prior art has taught gen Yam mm at plate (00% g 180180 .erally that smgle-stage drawmg exhibits the best g raii w mo at pie... 1.1:1 1.1:: ota raw Ratio 6.25:1 6.85: operability. g t z fi 36118.01 y .p. nu. EXAMPLE II Elongation (Per Cent) 9.2 6.0

The above table demonstrates that as the draw ratios increase, thetenacity increases also with a slight reduction in elongation. .Drawratios much in excess of 6:1 (for polyethylene terephthalate) are notpossible when the singlestage pin drawing procedure, as described in thework of Carothers, is used. For this reason, 'single-stagefdrawing"doesnot'devlop maximum tenacities. Furthermore, yarn drawn by hot tandem hotpin-hot plate proces's to the same draw-ratio as yarn drawn by thesingle stage pin drawing processexhibits a higher tenacity.

The increased draw ratio possible by doubledrawing for optimum qualityof yarn is shown in the' following table' The unstretched yarns wereidentical and made from polyethylene terephthalate having an intrinsicviscosity of 0.7, a T of 80 and a T1 of 99.2. The single-stage drawingand the initial draw of the double-drawing were both made at 85 C. Thesecond stage of the double-draw was carried out at 180 C.

Table V Yarn .A. B

Optimum Single Draw Ratio 5. 9:1 6.0:1 Optimum Double Draw Ratio- 6.6:1'6. 6:1 Single Drawn Dry Tenacity (g. p. 6.6 6. 8 Double Drawn DryTenacity (g. p. d.) & 7 2

1:1 Yarn B shows thatin the-zcase of polyethylene terephthalate,single-stage drawing, at a draw ratio "of Gi l/which is about maximumfor the "single-stage 'drawingof *thispolyester does not developmaximumwarn properties. From this it can be seen that by double-drawingthe draw "ratio for 'optimum' quality of yarn can be increased about10%. Furthermore, this increase is accompanied -'bya very appreciabletenacity increase.

Theimprovement to be realized by this inven- -tion-a's demonstrated byb'reaks per pound of yarn drawn issho'wn by a-comparison of a hot pinsingle-stage draw vs. the hot pin, hot plate tandem double-drawpreviously described in EX- -ample III. The following-table showscomparatively the improvement in the case of polyethylene terephthalateaswell as the improved 'yarn properties:

:rTable VI Draw Breaks, Tenacity, Elongation, Drawmg Method Ratio perlb. g./d. Per Cent Hot pin 5. 56:1 71.7 7.8 --6.-50 8.1 Hot pin-Hotplate tandem 5. 56:1 72. 6 1. 6 7. 02 ll. 4

KEY

' Yarn Identity l r '2 3 4 Polymer Intrinsic Viscosity -0. 7 -O. 7 0. 70.7 1st Stage Draw 813-80 C. Y 6.05:1 6.05:1 4. 92:1 4.92:1

2nd Stage Draw at 180 C 1.36:1 1.36:1 'TotalDraW 5.05:1 6 05:1 6.6216.6:1 Relaxation (Per- Dent) and Temperature. 10.0 (155) 0 (180) DrawnDenier 78 75 71 62 Dry Tenacityig. p..d.)- 6.4 6. 6 6. 7 7. 6

' Table VII Dry Teifierence nacity at From f Yarn Test fionditionseudoi' 1 Starting test ,(gIIlS Tenacity denier) (Per Cent) {2-8131}'Immersed in 2% H61 for 6 6.0 8,0 4DD weeks at room ateniperature. 7. 6,0. O {2SD Immersed-in 10% NaOHior l5 .2. 7 -59.0 4-DD days at roomtemperature. 7. 2 -5. O 1SD V 6.2 -4.0 0 Z-SD Exposed to room air at 90?C. 6.2 -.6.0 3DD for 4 weeks. 7 7.2 +8.0 4-1311. 7. 6 +1.0

The double-drawnryarns pf this invention have improved shrinkageproperties, The shrinkage, when double drawn yarns are heated totemperaturessuchas thosenormally experienced in washing and ironingfabrics, is to less than the shrinkage of single-drawn yarns- In thefol- :lowing. table thepreviouslymentibhed test yarns were tested forshrinkage:

Table -.VIII

1 Three min 1 i'iglne'half u es in our in yam boiling dry oven :waterair- C.

The drawing process of'this 'invention'also greatly increases themodulus of theyarn'i 'This is a very important factor whereyarnsof highstrength and 'high elasticity under heavy==loads are desired.Thefollowing is a'comparison of Youngsmodulus for two of the yarnspreviously mentioned:

Table IX Young's Modulus Yarn (grams per denier) 2-SD 73 4-LDD Waterabsorption of polyesterzfibers is.=very low so-that moisture causes noappreciable change in dimensions; When the yarn is wetted, it dries verquickly without shrinking.- The'yarns are not affected by customaryorganic solvents, nor b oxidizing agents or acids except in extremelyhigh concentrations. Ultra-violet light has little "effect upon theseyarns.'andinseets-=or microorganisms do not-attack it. The'yarns*exhibit a'highmodulus: and high impact strength.

.gives the fiber-forming polymer.

Becaus of the superior properties hereinabove disclosed, the yarnscomposed of synthetic linear polyesters and produced in accordance with.this invention areespecially adapted for use-as sewing .thread,particularly where high strength andrevsistance to chemicals, moisture,bacteria,.mil-

dew, etc., is desired. The yarn may be-made-into cords suitable for usein parachute shrouds and Webbing, cordage for use in the electroplatingindustry and for conversioninto rope which can be used for halyards,binding rope, glider tow rope, landing nets, fishing nets, or nets forsports such as tennis, badminton-or the like. Yarns may be woven orknitted intofabrics of allkinds and are-especially useful for a varietyofpurposes including fabrics for. window shades, Window curtains,balloon fabrics, parachute cloth, deck cloth for boats, airplane fabricsand canoe covers, sleeping bags, hunting coats, lifepreserver covers,

"War: map fabrics and bolting or screening cloths.

Because of its dimensional stability and dye resistance, fabrics for useinthe fabrication of jungle boots, jungle hammocks, automobile-tops,harvester aprons, mine blankets,.conveyorbelts,

especially where resistance to acid, insects, mil-p 4 dew, and bacteriain connection with high strength is desirable. Other industrial uses forwhich this yarn is suited are as filter cloths, separators and liners ofstorage batteries and insulating tapes. This fiber is also useful in thepreparation of fabrics used in underground mining works, for example, intubing for conveying air and other gases where high resistance to acidwaters is required. Fabrics composed of these yarns find use in themanufacture of fire hose because of their strength and resistance toabrasion. Since the yarns exhibit high resistance to stain and areunaffected by ultra-violet light, they are especially useful as tablelinens, aprons and the like where stainproofness is desirable, and foruse as zipper tapes, Venetian blind tapes, draperies and the like whereultra-violet resistance is important, Fabrics formed of these yarns and,if desired, .calendered and/or treated with a waterrepellent agent havea special utility in raincoats and shower curtains; or, if the weave ismade coarser, as mosquito netting and window screens. Since these fibersare, among other things, highly resistant to chemicals, they can be usedas mechanical packing, particularly in the form of a multifilament towor rope which is braided into a structure of the kind customarily usedfor packing joints surrounding moving shafts. Diaphragm fabrics for fuelpumps can also be prepared from the polyethylene terephthalate fibersdescribed herein.

Fabrics made from these yarns are extremely useful in the fabrication oflaminated structures. Excellent adhesive bonds are obtained betweenthese ethylene terephthalate polymers and various resins, syntheticrubbers and natural rubber. Fabrics of these yarns impregnated with ureaformaldehyde, phenol formaldehyde, melamine formaldehyde resins and thelike may be formed into laminated structures which have extraordinaryproperties of dimensional stability, resistance to moisture, highdielectric properties, etc., which make them useful for electricalinsulating purposes, instrument panels, parts for electrical devices ormechanical equipment and the like. Panels for structural purposes, wallboard, side wall material and bottom material for small boats, pontoonsand containers of various kinds can also be made from these laminatedmaterials.

Similarly, molded structures can be made by mixing staple or cut flockprepared from these ethylene terephthalate polymers with suitablebonding resins such as the urea formaldehyde type which can be molded byextrusion or pressure. Cable conduits, tubing, piping and numerous otherstructures can be made.

While yarns made from these polymers are capable of use wherever yarnshave previously been used with more or less advantage, there are certainfields where the properties of the polymer especially commendthemselves. For example, the high tenacity, flexibility and resilienceof the yarns of this invention make them suitable for use in themanufacture of hosiery and other articles of clothing, while theresistance to soiling and ease of cleaning (common cleaning agents maybe used on them without danger) make them desirable for use in flatfabrics and either as multifilament or monofilament yarns in themanufacture of pile fabrics including velvets, plushes, upholstery, orcarpeting. The yarns can be advantageously used as either the pileand/or backing of such fabrics.

14 At theysame'time their low .Water absorption, high resistance-to moldand bacteria growth and pronounced resistance to ultra-violet light makethe yarns highly suited for use in outdoor fab-- rics such as tents,awnings, tarpaulin, fla s, sails and the like. These same factors alsopermit the yarns to be manufactured into clothing and. other articlesfor use in tropical climates where light-weight flexible fabrics thatresist the action ever the light-weight, low water absorption and highresistance of the polymer to ultra-violet light, sulphur fumes and saltair are important attributes.

As many widely different embodiments of this invention may be madewithout departing from the spirit and scope thereof, it is understoodthat said invention is to be in no way delimited or restricted except asdefined in the appended claims. a

I claim:

1. The process of drawing shaped structures of synthetic linearpolyesters which comprises first drawing the shaped structure of asubstantially amorphous synthetic linear polyester at a temperaturebetween the second order transition temperature for said polyester andthe apparent minimum crystallization temperature for said polyesterdiscontinuing the draw while the polyester is in the amorphous state,heating the structure so drawn to a temperature above said apparentminimum crystallization temperature and further drawing said structureat said temperature above said apparent minimum crystallizationtemperature.

2. The process of drawing'yarn of synthetic linear polyesters whichcomprises first drawing yarn of a substantially amorphous syntheticlinear polyester at a yarn temperature between the second ordertransition temperature for said polyester and the apparent minimumcrystallization temperature for said polyester discontinuing the drawwhile the polyester is in the amorphous state, heating the yarn so drawnto a temperature above said apparent minimum crystallization temperatureand further drawing said yarn at said temperature above said apparentminimum crystallization temperature.

3. The process of claim 2 wherein the synthetic linear polyester ispolyethylene terephthalate.

4. The process of drawing yarn of synthetic linear polyester whichcomprises first drawing yarn of a substantially amorphous syntheticlinear polyester at a yarn temperature between the second ordertransition temperature for said polyester and the apparent minimumcrystallization temperature for said polyester discontinu ing the drawwhile the polyester is in the amorphous state, heating the yarn so drawnat a yarn temperature at least 50 C. higher than said apparent minimumcrystallization temperature and further drawingthe yarn at said yarntempera- 15= ture at least- 50 'CI' higherlthan' said apparent minimumciystallization: tempeiature.

5. The process of claim: 4 wherein: the syn-v theti'c 'linear'polyester' is polyethylene terephthalatel 6. The process of drawingyarn ofsynthetic linear polyester which comprises first drawing a yarnof a substantially amphorous synthetic: linea polyester having anintrinsicviscosity of at least-0.3 at a yarn temperature between thesecond order -"transition temperature for said polyesten and theapparent minimum crystallization temperature for said polyestediscontinuing the draw while the polyester-is inthe amorphous state;heating the yarn sodrawn to a temperature above said-apparent minimumcrystallization temperatureand further drawing said yarn'at said:temperature above said :apparent' minimum"- crystallization temperature.

'7. Theproce'ss' of claim 6 wherein the syn;

thetic linear polyester is polyethylene terephthalate.

8. The process-of drawing yarn" of synthetic linear polyester whichcomprises'first drawing a yarn of a substantially amorphous synthetic 1linear polyester having an intrinsic Viscosity of fromO.3 to 1.5, at ayarn temperature between the secondorder-transition temperature for saidpolyester and the apparent minimum crystallization temperature for saidpolyester discontinuing the draw while the polyester isin'the amorphousstate, heating the yarn so drawn at a yarn temperature at least 50 C.higher than said apparent'minimum .crystallizationetemperature and": *1further. drawing the yarnat-said yarn'temperaa? ture' at" least 50 C.higherthanrsaid. apparent-* minimum crystallization temperaturethe firstdrawing constitutingthe major proportion of the total draw.

9. The process of claim 8 wherein 'tl'ie yarn" is drawn a total offrom3' to 10 times its original length;

10. The process'of claim 8" wherein the yarn is drawn a totaloffrom5-to'8 times its original-- length.

11. The process ofmlaim '10 wherein the syn-" thetic linear polyester:is" polyethylene terephthala'tep ANDERSON PACE, JR.

REFERENCES CITED The following'references are of record in the 1 file oi-this patent:

UNITED STATES PATENTS? i OTHER REFERENCES Wiley, Transition TemperatureandCubical Expansion of Plastic'Materialsf" Ind;"'& Eng;

CheniL, Sept. 1942;pages 1052-6.

1. THE PROCESS OF DRAWING SHAPED STRUCTURES OF SYNTHETIC LINEARPOLYESTERS WHICH COMPRISES FIRST DRAWING THE SHAPED STRUCTURE OF ASUBSTANTIALLY AMORPHOUS SYNTHETIC LINEAR POLYESTER AT A TEMPERATUREBETWEEN THE SECOND ORDER TRANSITION TEMPERATURE FOR SAID POLYESTER ANDTHE APPARENT MINIMUM CRYSTALLIZATION TEMPERATURE FOR SAID POLYESTERDISCONTINUING THE DRAW WHILE THE POLYESTER IS IN THE AMORPHOUS STATE,HEATING THE STRUCTURE SO DRAWN TO A TEMPERATURE ABOVE SAID APPARENTMINIMUM CRYSTALIZATION TEMPERATURE AND FURTHER DRAWING SAID STRUCTURE ATSAID TEMPERATURE ABOVE SAID APPARETN MINIMUM CRYSTALLIZATIONTEMPERATURE.